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Taking a two-week course of metformin, a safe and affordable diabetes medication, after testing positive for SARS-CoV-2, may lead to 40 per cent fewer long Covid risk, according to a results of trial published in The Lancet Infectious Diseases journal.

Currently, there are no proven treatments or ways to prevent long Covid, other than reducing the risk of infection in the first place.

The phase 3 trial is the first to show a medication that can reduce the risk of long Covid when taken after testing positive for SARS-CoV-2, said researchers from University of Minnesota, US.

However, the results do not indicate whether metformin would be effective as a treatment for those who already have long Covid, they said.

"Long Covid is a significant public health emergency that may have lasting physical health, mental health, and economic impacts, especially in socioeconomically marginalised groups. There is an urgent need to find potential treatments and ways to prevent this disease," said first author Dr Carolyn Bramante from the varsity's Medical School.

"Previous studies have found that metformin stops the SARS-CoV-2 virus from replicating in the lab, which is consistent with predictions from our mathematical modelling of viral replication, so that might be what is causing the reduction in both severe Covid-19 and long Covid diagnoses seen in this trial," said co-author David Odde, a biomedical engineer at University of Minnesota.

The study included 1,126 patients who were given either metformin or an identical placebo pill after testing positive for SARS-CoV-2 between December 2020 to January 2022. Participants were followed up for 10 months with data gathered by self-report questionnaire every 30 days.

In the trial, 6.3 per cent (35/564) of participants given metformin reported a long Covid diagnosis within 10 months of follow up, compared to 10.4 per cent (58/562) of those receiving an identical placebo.

These findings reflect previously published results from this trial which found metformin prevented over 40 per cent of emergency department visits, hospitalisations, and deaths due to Covid within two weeks of starting the treatment, compared to a placebo.

Other arms of the trial looked at ivermectin and fluvoxamine and found that neither prevented long Covid.

The researchers also acknowledge some limitations to the study, including that the trial excluded those with a BMI under 25 and those younger than 30 years, and therefore it is unknown if these findings could be generalised to those populations.

"If confirmed, the findings are profound and potentially landmark (a) this is the first high-quality evidence from a randomised controlled trial to show that the incidence of long Covid can be reduced by a medical intervention, metformin -- an inexpensive treatment with which clinicians have ample experience," said Dr Jeremy Faust of Harvard Medical School, who was not involved in this research